Aperture 3 could be used for batch conversion. You import the RAW pictures into a library. When importing you could have a set of pre-defined settings. Choose Import Settings -> Adjusment Preset. Select the preset you like. If there is no one that you like, you could edit/create your own preset. During the import process it is also possible to do a backup of your files, which I think is handy. Of course you could do simple things like renaming pictures etc. When you have them all imported, you could export them at once or apply your adjustment.

The process is semi-automatic, you will have to select the settings before import and the choose your settings when exporting. If you want to automate everything, I suggest using the Automator application that is provided with Mac OS X.

I use Aperture 3 for batch processing and a like a lot. It is cheaper than PhotoShop. It is available for Mac OS X.

This does not answer the question, which was about performing batch operations on RAW files and conversions into JPEG. When answering, don't just look at other answers, make sure you are actually answering the question.
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jrista♦Feb 7 '12 at 17:58

OK, I have tried to clarify the answer. For me this was obvious in the context of mentioning a software that could help with batch conversion ;-) I hope that it is clear now.
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Johan KarlssonFeb 7 '12 at 18:24

As I don't have any extra photo editing programs I used iPhoto to do this.
Open iPhoto with the option key held down. This gives you the option to create a new library. Create a temporary one somewhere where it will be easy to find and delete it later. Import all the Raw Pictures into the new library. Export them all in the required format. Quit and delete the library.

ACDSee Pro is a good tool. It is available for Windows and Mac OS X. I used this for many years. It has good batch processing engine. It is very handy to do these type of batch conversion, batch re-size, batch rename, batch color correction etc.

I would go with Adobe Lightroom. You can process catalog, set of photos or photo by clicking "File > Export.." and set not only dimension of photos but also add watermark, sharpen them for printing or screen, rename and much more.

It's also great tool for editing photos and applying same styles for all photos take literally seconds.